210 TRANSACTIONS AND PEOCEEDIXGS OF THE [Sess. lviii. 



Ill these experiments four results are recorded in favour 

 of light and four in favour of obscurity; though the excess 

 in favour of obscurity is rather more than twice as great 

 as that recorded in favour of light. 



This leaves a total excess of carbonic anhydride pro- 

 duced in favour of obscurity of 1"47 CO., or I'l-l per cent, 

 on the mean of the total quantity of carbonic anhydride 

 produced in all the experiments. 



The rate of increased activity in favour of obscurity, 

 thus obtained, approaches in amount that found in the 

 first series of experiments. 



This result, if considered trustworthy, seems to bear out 

 the explanation given above of the considerable discrepancy 

 between the evidence afforded by the results of the first 

 and second series of experiments as to the influence of 

 light on the respiration of germinating barley. 



A noteworthy point in this third series of experiments 

 is the fact that although the contamination of the air by 

 carbonic anhydride is much greater than it was in the first 

 series, yet its effect in masking the stimulating action of 

 light is not increased, as might reasonably be expected 

 would be the case. The only part of the seed which would 

 probably have the power of decomposing carbonic anhydride 

 in presence of light is the young plumula, and the quantity of 

 this gas which it would be able to decompose would certainly 

 be very small, so it might happen that when the amount of 

 carbonic anhydride present in the air is above a certain 

 point it ceases to have an increased effect in diminishing 

 the observed quantity of the gas which is produced by the 

 seeds when germinated under the influence of light. 



It seems fair to conclude from a consideration of all 

 the results obtained that light has probably a small 

 stimulating action on the respiration of germinating barley, 

 resulting in an increase of between 3 and 4 per cent, in 

 the quantity of carbonic anhydride excreted ; and that 

 this increased activity is lost sight of when the air 

 surrounding the seeds is contaminated, even in a small 

 degree, by carbonic anyhdride. 



I made a few experiments to ascertain the influence of 

 light on the respiration of germinating wheat, employing 



